U.S. stocks tumbled Friday to their biggest loss in more than seven months, extending a global selloff that investors fear signals turmoil to come as financial markets adjust to a pullback in central-bank stimulus.

The declines extend a dark beginning of the year for equity investors world-wide, a jarring drop for markets that climbed...

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Emerging-market currencies are getting hammered around the globe, and the rout is forcing investors and traders to also sell other assets, like U.S. stocks, to cover their losses. FiREapps CEO Wolfgang Koester says it could be trouble for multinationals. Photo: Getty Images.